1. Field of the Invention
The present invention relates to an image forming apparatus forming an image in accordance with control codes stored in a memory medium, and a rewrite control method for the image forming apparatus.
2. Description of the Related Art
Hitherto, memory media such as ROMs (Read Only Memories) have been employed as memory means for storing control codes used for control of image forming apparatus. Rewritable memory media such as flash ROMs have also been employed in recent years. Control codes are rewritable by transferring data to such a rewritable memory medium from an external apparatus, e.g., a host computer.
In the conventional techniques, however, a rewrite process must have been carried out for a plurality of flash ROMs for completing rewrite, and a large amount of download programs have been required to be written in the ROMs or the like. Therefore, programs are more likely to contain bugs, and if bugs are found in ROMs or the like, those ROMs must be replaced. This has accompanied the problem of imposing a large load on rewrite work.
Also, the conventional techniques have had another problem in the rewrite process. Because of an interrupt area being used in common to image forming control, an interrupt area dedicated for the rewrite process cannot be secured. Accordingly, it is indispensable to monitor at all times whether data is transmitted from an external apparatus, meaning that the rewrite process takes a longer period of time.
Meanwhile, it is also known to store a rewrite program, which is necessary for carrying out rewrite of control programs transmitted from an external apparatus, not in a flash ROM where information slightly tends to be unstable, but in a ROM.
In such a case, a CPU (Central Processing Unit) executes various processes while controlling respective components in accordance with the rewrite program preset in a ROM.
Control programs are stored in a nonvolatile readable/writable ROM, allowing new control programs to be written in that ROM. On the other hand, a rewrite program used for down-loading the control programs is fixedly held in a memory medium which is not updated. In other words, changes of the rewrite program have not been taken into consideration.
As an example of the situation described above, in copying machines, printers and so on, control programs have been stored in a nonvolatile EPROM (Erasable Programmable ROM) or a mask ROM, but it has become common that a flash ROM, an EEPROM (Electrically Erasable Programmable ROM), etc., which are nonvolatile memories being readable and writable on-board, are employed so that the rewrite program can be updated without replacing the ROM by a new one when addition of functions or version-up of an application program will be necessary in future.
More specifically, when the rewrite program in a flash ROM is updated, a new rewrite program is downloaded into the flash ROM from a host computer, a CD-ROM drive, a floppy drive or the like which is connected to an image forming apparatus.
To this end, communication means is provided in the image forming apparatus, and a rewrite download program adapted for the image forming apparatus is held in a memory medium which is disposed in the apparatus and not updated.
In the conventional image forming apparatus, however, because the rewrite download program is fixedly held, control programs to be down-loaded have been restricted by the rewrite download program.
Further, because a manner of down-loading control programs is also determined by the rewrite download program, flexibility in a manner of download is small; hence it has been difficult to perform efficient download.
In the above method, for example, changing addresses of a ROM, into which control programs are to be down-loaded, has not been taken into consideration, and new control programs are down-loaded within the range of an address area originally assigned for the control programs in advance. Accordingly, if new control programs which are different in, e.g., assignment address area from the original control programs are down-loaded, the rewrite download program built in the image forming apparatus and the download application operating on the host computer cannot be utilized due to a difference in address configuration. In such a case, the ROM storing the rewrite download program must be replaced and hence the efficiency of rewrite work is lowered.
Additionally, where the rewrite download program is stored in a memory medium (e.g., a mask ROM) which is disposed in the image forming apparatus and not updated, that ROM must be replaced if there occurs any failure in the rewrite download program.